The purpose of this study is to help determine the safety and efficacy of an experimental Salmonella typhi vaccine which is combined with an antigen from either cholera, hepatitis, or traveler's diarrhea. The vaccine is oral, and the Salmonella typhi is live but greatly weakened. The primary focus of this work is to determine wether it is possible to generate a serological immune response to these heterologous antigens expressed in an immunogenic vaccine strain in humans, i.e. is it possible to use this strain as a bivalent vaccine capable of inducing immunity against the bacterial vector as well as a carried antigen. Previous studies on the GCRC have established the safety and immunogenicity of the recombinant salmonella vaccine. No signs of infection or prolonged colonization occurred, and immune studies demonstrated that serum antibody (IgG) levels appear to be at protective levels. The current studies will examine whether the oral administration of the S. typhi vaccine which has been engineered to contain heterologous antigens (see above) results in effective immunization. The convenience and theoretical advantages of using oral s. typhi as a "vector" for vaccination against a variety of diseases (including AIDS) are very appealing. This study will examine the safety and efficacy of the recombinant experimental vaccines.